on leaving Lake St. Clair, it should be rich at Station 126, unless 

 poisonous substances derived from sewage killed the organisms. On 

 the other hand, if the water were poor in plankton on leaving 

 Lake St. Clair, one would expect it to be poor at Station 126. 



The results of Reighard's work on the plankton seemed to 

 point toward the second explanation, namely, that the lower river 

 was poor in plankton because Lake St. Clair was poor. In spring 

 of 1893 he took samples in the upper part of the river and fo\ind 

 little plankton as compared with Lake Michigan (Reighard, 1893). 

 In September of the same year he found threi^ times as much plankton 

 per unit volume of water near the islands of Lake Erie as in 

 Lake St. Clair, A single sample in Lake Erie near Detroit River 

 yielded less than one eighth the average amount near the islands 

 (Reighard, l89ii). Osburn (1926a) also noted the scarcity of 

 plankton at the mouth of Detroit River, 



In the present investigation it was impossible to study the 

 situation in detail, because of the distance of Lake St. Clair from the 

 base of operations. However, a trip was made to the lake on 

 September 23, 1930, and samples were taken at a point near Reighard's 

 Station VIII, where the depth was 3.9 meters. Samples at and 3 

 meters yielded average counts (in thousands of units per liter) as 

 follows: diatoms, l8j greens, 27; blue-greens, 66; and others, 3. 

 These counts are very low for diatoms, greens, and blue-greens as 

 coiTipared with the average for the Island Section in late September 

 (Table 53). Surface and bottom samples were taken at Station 126 

 about five hours after the Lake St, Clair samples. Reference to 

 Table 60 shows that the counts of greens and blue-greens were lower 

 than those in Lake St. Clair, while that of diatoms was higher. 



It sho'i/ld be mentioned that the water sampled at Station 126 

 was not the same water sampled in Lake St. Clair, for it takes more than 

 five hours for the water to travel from Lake St. Clair to Lake Ei-ie, 

 Hence, the lack of agreement in counts between the two stations is not 

 surprising, especially since plankte-? may die and others may come in 

 from marginal waters. 



The evidence presented here agrees with Reighard's evidence 

 in indicating that Lake St. Clair is poor in plankton. This conclusion, 

 based on a study of the phytoplankton alone, as well as the total 

 plankton (Reighard), is supported by evidence from the zooplankton alone 

 (page 238), The results do not permit a definite statement regarding 

 the fate of the plankton of Lake St. Clair in its travel doim Detroit 

 River, j'-et there are three good reasons for believing that pollution 

 does not affect the plankton adversely. The reasons are as follows: 



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